Fix pip issues on AppVeyor CI (#1369)

.appveyor.yml

@@ -41,8 +41,8 @@ install:
     if ($env:PYTHON) {
       if ($env:PLATFORM -eq "x64") { $env:PYTHON = "$env:PYTHON-x64" }
       $env:PATH = "C:\Python$env:PYTHON\;C:\Python$env:PYTHON\Scripts\;$env:PATH"
-      pip install --disable-pip-version-check --user --upgrade pip wheel
-      pip install pytest numpy
+      python -m pip install --upgrade pip wheel
+      python -m pip install pytest numpy --no-warn-script-location
     } elseif ($env:CONDA) {
       if ($env:CONDA -eq "27") { $env:CONDA = "" }
       if ($env:PLATFORM -eq "x64") { $env:CONDA = "$env:CONDA-x64" }